A Radio Astronomy Search for Cold Dark Matter Axions

Abstract

The search for axions has gained ground in recent years, with laboratory searches for cold dark matter (CDM) axions, relativistic solar axions and ultra-light axions the subject of extensive literature. In particular, the interest in axions as a CDM candidate has been motivated by its potential to account for all of the inferred value of $\Omega_{DM} \sim 0.26$ in the standard $\Lambda CDM$ model. Indeed, the value of $\Omega_{DM} \sim 0.26$ could be provided by a light axion. We investigate the possibility of complementing existing axion search experiments with radio telescope observations in an attempt to detect axion conversion in astrophysical magnetic fields. Searching for a CDM axion signal from a large-scale astrophysical environment provides new challenges, with the magnetic field structure playing a crucial role in both the rate of interaction and the properties of the observed photon. However, with a predicted frequency in the radio band (200MHz - 200GHz) and a distinguishable spectral profile, next generation radio telescopes may offer new opportunities for detection. The SKA-mid telescope has a planned frequency range of 0.4 - 13.8GHz with optimal sensitivity in the range $\sim$ 2 - 7 GHz. Considering observations at $\sim 500$MHz, the limiting sensitivity is expected to be $\sim 0.04$mK based on a 24 hour integration time. This compares with a predicted CDM axion all-sky signal temperature of $\sim 0.04$mK using SKA Phase 1 telescopes and up to $\sim 1.17$mK using a collecting area of (1km)$^2$ as planned for Phase 2.